Thursday, December 1, 2016

Ukraine moves giant new safety dome over Chernobyl nhưng cũng chỉ hy vọng ngăn phóng xạ thoát ra trong thời gian chừng 100 năm, sau đó thi sao?

Mái vòm kim loại cũng chỉ hy vọng ngăn phần nào phóng xạ không thoát ra không trung trong thời hạn 100 năm, trong khi tác hại của phóng xạ nguyên tử kéo dài hàng ngàn năm!
Ukraine moves giant new safety dome over Chernobyl

By Oleksandr SAVOCHENKOChernobyl, Ukraine (AFP) Nov 29, 2016

Nuclear cover up: Chernobyl's giant domeParis (AFP) Nov 29, 2016 - The new metal dome encasing Ukraine's infamous Chernobyl nuclear power plant contains enough metal to build three Eiffel Towers with a few thousand tonnes to spare.At 108 metres (354 feet) it is taller than the Statue of Liberty and is designed to contain the power plant's dangerous radioactivity while protecting the plant from climactic events for the next century.
The giant dome was fitted 20 years after Chernobyl reactor number four exploded on April 26, 1986, spewing poisonous radiation over large parts of Europe, particularly Ukraine, Belarus and Russia.
The European Bank for Reconstruction and Development (EBRD) is leading the 2.1 billion euro (2.2 billion dollars) project, with contributions from around 40 countries.
The metal dome, built in Italy, rests on a foundation of rectangular concrete beams and weighs 36,000 tonnes, three and a half times the weight of the iconic Eiffel Tower in Paris.
The 162-metre-long 30-storey high structure now covers an original sarcophagus hurriedly put in place by Soviet workers known as "liquidators", after the worst nuclear accident in history.
- Many 'liquidators died' -
Over 600,000 "liquidators" were sent to the scene of the accident with little or no protection over four years.
Many died attempting to extinguish the initial fire, isolate the destroyed reactor under concrete and clean up the surrounding area.
The new casing has two objectives: "to contain the radioactive dust and to allow the future dismantling of the damaged reactor as well as the reprocessing of the 200 tonnes of highly radioactive magma from the old sarcophagus" which has reached the end of its useful life, said the project's director, Nicolas Caille.
Caille, who works for Novarka, the joint venture by French construction firms VINCI and Bouygues which built the dome, hailed it as "a feat of engineering that will ensure optimal safety conditions for the Ukrainian people for the next 100 years."
The structure has equipment and facilities to allow the reactor to be dismantled while limiting the need for human intervention, as the dome will be sealed off hermetically, according to Novarka.
The ventilation system controls the atmosphere inside, regulating the temperature and humidity levels.
The equipment is now due to be tested and completed before a handover to Chernobyl nuclear authorities expected in November 2017.
- Designed to withstand earthquakes -
The construction of the "New Safe Confinement", as the dome is called, is hailed by organisers as one of the world's most ambitious engineering projects.
Up to 1,220 Ukrainian workers were employed on the site during the "peak period", with a total of 2,500 workers taking part, the teams alternating 15 days on the site and 15 days off to keep exposure to radioactivity "still well below the safety standards set by the nuclear safety authorities," according to the company.
The dome is designed to withstand temperatures ranging from -43 to +45 degrees Celsius and a category 3 storm -- now unlikely in Ukraine, but considered "in case of global warming," Caille told AFP.
And while there is "a low seismic risk" in the country, the structure is also built to resist a strong earthquake, so that even if the concrete sarcophagus were to collapse the metal casing would remain intact.
So far the EBRD has raised 1.5 billion euros from the G7 group of leading economies and international donors. But it is Ukraine which must bear the running costs of the project.
"Much investment will still be needed to bury the radioactive materials that will be recovered," said Olexi Pasyuk of the Ukrainian National Center for Ecology.
Ukraine on Tuesday unveiled the world's largest moveable metal structure over the Chernobyl nuclear power plant's doomed fourth reactor to ensure the safety of Europeans for future generations.
The gigantic arch soars 108 metres (355 feet) into the sky -- making it taller than New York's Statue of Liberty -- while its weight of 36,000 tons is three times heavier than the Eiffel Tower in Paris.
The 2.1-billion-euro ($2.2-billion) structure sponsored by the European Bank for Reconstruction and Development (EBRD) has been edged into place over an existing crumbling dome that the Soviets built in haste when disaster struck three decades ago.
Ukrainian President Petro Poroshenko was visibly proud at his impoverished and war-torn country's ability to deal with one of the worst vestiges of its Soviet past.
"Many people had doubts and refused to believe that this was possible," Poroshenko told the festive ceremony held in front of the gleaming new dome.
"But my friends, I congratulate you -- yes, we did it!"
- 'Super-human efforts' -
Radioactive fallout from the site of the world's worst civil nuclear accident spread across three-quarters of Europe and prompted a global rethink about the safety of atomic fuel.
Work on the previous dome began after a 10-day fire caused by the explosion was contained but radiation still spewed out of the stricken reactor.
"It was done through the super-human efforts of thousands of ordinary people," the Chernobyl museum's deputy chief Anna Korolevska told AFP.
"What kind of protective gear could they have possibly had? They worked in regular construction clothes."
About 30 of the cleanup workers known as liquidators were killed on site or died from overwhelming radiation poisoning in the following weeks.
The Soviets sought to try to cover up the accident that was caused by errors during an experimental safety check and its eventual toll is still hotly disputed.
The United Nations estimated in 2005 that around 4,000 people had either been killed or were left dying from cancer and other related diseases.
But the Greenpeace environmental protection group believes the figure may be closer to 100,000.
Authorities maintain a 30-kilometre-wide (19-mile) exclusion zone around the plant in which only a few dozen elderly people live.
- 30-year lifespan -
One of the main problems of the Soviet-era response was the fact that it only had a 30-year lifespan.
Yet its deterioration began much sooner than that.
"Radioactive dust inside the structure is being blown out through the cracks," Sergiy Paskevych of Ukraine's Institute of Nuclear Power Plant Safety Problems told AFP.
Paskevych added that the existing structure could crumble under extreme weather conditions.
The new arch should be able to withstand tremors of 6.0 magnitude -- a strength rarely seen in eastern Europe -- and tornados that strike the region only once every million years.
- Long time coming -
Kiev has complained that European assistance was slow to materialise.
The EBRD found 40 state sponsors to fund a competition in 2007 to choose who should build the massive moveable dome.
A French consortium of two companies known as Novarka finished the designs in 2010 and began construction two years later.
The shelter was edged towards the fourth reactor in just under three weeks of delicate work this month that was interrupted by bad weather and other potential dangers.
It will later be fitted with radiation control equipment as well as air vents and fire fighting measures.
The equipment inside the arch is expected to be operative by the end of 2017.
"Only then will we begin to disassemble the old, unstable structure," State Nuclear Regulatory Inspectorate of Ukraine's head Sergiy Bozhko told AFP.
But he said no timeframe had yet been set for the particularly hazardous work of removing all the remaining nuclear fuel from inside the plant or dismantling the old dome.
Novarka believes that its arch will keep Europe safe from nuclear fallout for the next 100 years.

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